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MRCOG - Part 1 > Biophysics > Flashcards

Biophysics Flashcards

1
Q

What does the p wave represent on an ECG?

A

Atrial depolarisation

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2
Q

What does the QRS represent on an ECG?

A

Ventricular depolarisation (atrial repolarisation takes place at the same time)

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3
Q

What does the T wave present on an ECG?

A

Ventricular repolarisation

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4
Q

At what rate is an ECG recorded?

A

25mm/second

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5
Q

How long does a large square on an ECG represent?

A

0.2 seconds

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6
Q

How long does a little square on an ECG represent?

A

0.04 seconds

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7
Q

Which leads measure electrical heart activity in the frontal plane?

A

Limb leads (I, II, III) and augmented voltage leads (aVR, AVL, aVF)

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8
Q

Which leads measure electrical heart activity in the horizontal plane?

A

Chest leads - V1-V6

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9
Q

Which leads represent the lateral heart?

A

I, aVL, V5-V6

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10
Q

Which leads represent the septal part of the heart?

A

V1-V2

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11
Q

Which leads represent the anterior part of the heart?

A

V3-V4

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12
Q

Which leads represent the inferior heart?

A

II, III, aVF

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13
Q

What is the normal duration of the PR interval?

A

0.12-0.2 seconds

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14
Q

What is the normal duration of the QRS interval?

A

<0.12 seconds

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15
Q

What are the advantages of USS?

A

1) Non-invasive

2) Does not use ionising radiation

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16
Q

What are the functions of USS?

A

1) Determining the nature of tissues, e.g. cystic vs. solid
2) Assessing movement of tissues
3) Measurement of blood flow
4) Measurement of structures

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17
Q

At what frequencies are sound waves considered ultrasound?

A

Frequencies >20kHz

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18
Q

What is the frequency range used in abdominal USS?

A

1-5 MHz

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19
Q

What is the frequency range used in transvaginal USS?

A

5-10 MHz

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20
Q

How is ultrasound generated?

A

By generation of a pressure wave - a pressure wave being generated by a piezoelectric crystal placed in the transducer that contacts tissue under investigation. Piezoelectric crystals convert electrical energy to mechanical energy.

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21
Q

What are the 2 types of ultrasound?

A

1) Continuous-wave ultrasound

2) Pulsed-wave ultrasound

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22
Q

Which type of ultrasound is used for imaging purposes?

A

Pulsed-wave ultrasound

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23
Q

What are the three principle interactions of ultrasound with tissue?

A

1) Reflection
2) Scatter
3) Absorption

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24
Q

What tissue properties determine the degree of reflection?

A

The acoustic impedance - which is the density if the tissue (p), multiplied by the velocity of ultrasound in that particular tissue (c)
Z = p x c
The greater the difference in acoustic impedance between tissues, the greater the degree of reflection.

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25
Q

When does scatter occur?

A

When ultrasound interacts with structures with smaller dimensions than the wavelength of the ultrasound wave.

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26
Q

What is absorption with regard to ultrasound?

A

Absorption is the conversion of mechanical (ultrasound) energy into heat. Absorption increases with frequency.

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27
Q

What are the limitations of real-time (B-mode) USS scanning?

A

1) Inadequate spatial resolution
2) Inadequate penetration
3) Poor image quality
4) Low frame rate
5) Compromised field of view
6) Low line density

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28
Q

What is spatial resolution?

A

= the min distance between two reflectors that is necessary to be able to distinguish two separate echo signals.

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29
Q

What is spatial resolution determined by?

A

1) Axial resolution - determined by pulse length
2) Lateral resolution - determined by beam width
3) Slice thickness - determined by thickness of the transducer and therefore transducer design.

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30
Q

What factors influence ultrasound penetration?

A

Absorption and scatter
Absorption and scatter both increase with increased frequencies and therefore better penetration requires lower frequencies (and therefore better penetration = poorer resolution)

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31
Q

What information can doppler ultrasound yield?

A

1) Speed at which the target is moving

2) Direction of the motion

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32
Q

What is doppler frequency shift?

A

The difference in frequency between the returning echo and the transmitted ultrasound wave. It is used to assess blood flow.

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33
Q

What is a colour flow scanner?

A

Combines real-time B-mode imaging ultrasound with pulsed-wave doppler and colour flow imaging. Used to assess blood flow.

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34
Q

What does red on a colour flow scanner represent?

A

Flow TOWARDS the transducer

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35
Q

What does blue on a colour flow scanner represent?

A

Flow AWAY from the transducer

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36
Q

How are differing velocities represented on colour flow scanners?

A

Dark hues = low velocity

Bright hues = high velocity

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37
Q

What are the bioeffects of ultrasound?

A

1) Heating

2) Cavitation

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38
Q

What is the ‘thermal index’ with regard to ultrasound?

A

It is an estimate of the rise in tissue temperature that might be possible in a ‘reasonable worst-case scenario’. The operator should continually monitor the thermal index and keep it as low as is consistent with achieving a diagnostic result.

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39
Q

What are the three types of thermal index?

A

TIS - thermal index in soft tissues
TIB - thermal index in bone
TIC - thermal index in cranium

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40
Q

Which type of thermal index should you be monitoring in O&G?

A

TIS in scans in first 8/40

TIB in all other and subsequent scans

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41
Q

What is cavitation?

A

The lysing/damage of cells as a result of ultrasound

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42
Q

What is the wavelength rage of an x-ray?

A

10-0.1nm

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43
Q

What is the energy range of an x-ray?

A

120eV to 120keV

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44
Q

What is the difference between soft and hard x-rays?

A

Soft x-rays = energy <12keV

Hard x-rays = energy >12keV

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45
Q

How are x-rays produced?

A

Accelerating electron collide with a metal target — deceleration on collision results in electrons from the inner shell of the metal atom being knocked off —electrons from higher energy levels fill up the space and x-ray photons are emitted as a result?

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46
Q

What are the advantages of computed x-rays?

A

1) Do not require on-site wet processing facilities
2) Do not require non-renewable silver
3) Easier archiving/retrieval of images
4) Space-saving

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47
Q

What is the radiation dose of a hysterosalpingogram?

A

1mSv = 4 months of background radiation

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48
Q

What are the advantages of hysterosalpingogram?

A

1) Complications rare
2) Relatively quick
3) Valuable information re: tubal patency

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49
Q

What are the risks of hysterosalpingogram?

A

1) Small risk of cancer from radiation exposure
2) Flare-up of undiagnosed chronic PID
3) inadvertent exposure of an unsuspected early pregnancy to radiation
4) Small teratogenic risk associated with ovarian radiation

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50
Q

What is CT used for in gynaecology?

A

Assessment of pelvic tumours

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51
Q

How does MRI work?

A

Magnetic field aligns protons present in the water (H2O) molecules of tissues — a radiofrequency pulse is then used to disrupt the alignment of these protons — following the pulse the protons drift back into alignment emitting a detectable radiofrequency signal

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52
Q

How does spatial resolution in MRI compare to CT?

A

Spatial resolution - the ability to distinguish between two structures very close together as separate - is comparable to that of CT

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53
Q

How does contrast resolution in MRI compare to CT?

A

Contrast resolution - the ability to distinguish between two similar but not identical tissues - is better in MRI compared to CT

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54
Q

What is the current view on contrasts used in MRI in pregnancy?

A

Gadolinium-based agents are known to cross the placenta, however they appear to be safe, any gadolinium reaching the fetus being rapidly eliminated in urine. Therefore, such studies should be considered if important for the health of the mother

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55
Q

What type of USS surgery is MRI guided?

A

Uterine fibroids - MRI being used to target ultrasound beams. Ultrasound increases tissue temp to >65 degrees C, destroying it.

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56
Q

What are the disadvantages of MRI?

A

1) Claustrophobia
2) Noisy
3) Contraindicated in those with metal clips/pacing wires/metal fragments etc.

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57
Q

How does a diathermy machine work?

A

Converts mains low-frequency current - approx. 50Hz - into high frequency current ranging 200kHz-3.3MHz.

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58
Q

What can be achieved by diathermy?

A

Cutting, coagulation, vaporisation and/or destruction.

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59
Q

What is monopolar surgical diathermy?

A

The electric current is transported through the human body and back to the generator.
The electrode may take the form of a blade, ball, are needle tip or a loop.

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60
Q

What is bipolar diathermy?

A

When the current flow between the tips of forceps blades. One blade acts are the active electrode, the other as a return.

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61
Q

What are the differences in what can be achieved by monopolar vs. bipolar diathermy?

A 
Monopolar = cutting or coagulations
Bipolar = coagulation only
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62
Q

What type of electric current is used for cutting modes?

A

A low voltage continuous unmodulated sinusoidal waveform.
Electric arcs form between the tissue and the cutting electrode just above the tissue, produces a temperature such that cells are vaporised and a clean cut is achieved.

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63
Q

What type of electric current is used for coagulation modes?

A

A high voltage current that is applied intermittently and modulated with a duty current - the modulation (or dampening) allows the tissue to cool between heating bursts and so no vaporisation occurs

64
Q

What is fulguration?

A

When high-powered current is used to produce a sparking effect to coagulate a large bleeding area or to char a tissue without touching it. Produces a deeper coagulation and is used in specific circumstances only.

65
Q

Which is safer, monopolar or bipolar diathermy?

A

Bipolar

66
Q

What are the hazards associated with monopolar diathermy?

A

1) Direct coupling
2) Insulation failure
3) Capacitive coupling

67
Q

What is direct coupling?

A

When electrode activated next to/in contact with another conductive instrument in the body

68
Q

What is insulation failure?

A

When the coating that covers the active electrode is compromised

69
Q

What is capacitive coupling?

A

May occur between two conductors separated by an insulator - the electric current can be passed through the insulation into the other conductor and the electrical energy can be discharged into tissue structures it is in contact with

70
Q

What does ‘LASER’ stand for?

A 
Light
Amplification by
Stimulated
Emission of
Radiation
71
Q

What are the different types of lasers?

A

1) Gas - e.g. CO2 or argon

2) Solid-state

72
Q

What is the wavelength of CO2 lasers?

A

10 600nm

73
Q

Are CO2 lasers suitable for laparoscopic surgery?

A

No, because their depth is very limited

74
Q

What are the limitations of external beam radiotherapy?

A

1) Inability to identify microscopic disease accurately
2) Difficulty in immobilising the treated person/tumour
3) Problems arising from tumour shrinkage

75
Q

What are the different forms of internally-delivered radiotherapy?

A

1) Sealed-source radiotherapy

2) Unsealed-source radiotherapy

76
Q

Which type of internal-beam radiotherapy is brachytherapy?

A

Sealed-source

77
Q

In what types of gynaecological cancer is brachytherapy used?

A

Vaginal, cervical, ovarian and uterine

78
Q

Which isotopes are used in gynae brachytherapy?

A

Caesium-137

Iridium-192

79
Q

What type of internal-beam radiotherapy is radioisotope therapy?

A

Unsealed-course (delivered by injection)

80
Q

What are the acute adverse effects of radiotherapy?

A

1) Damage to epithelial surfaces
2) oedema and swelling of soft tissues
3) Infertility
4) Generalised fatigue

81
Q

What are the medium/long-term effects of radiotherapy?

A

1) Fibrosis and scarring or irradiated tissues
2) Hair loss
3) Dryness
4) Fatigue and lethargy
5) Cancer secondary to irradiation
6) Death

82
Q

How is oligohydramnios defined on scan?

A

AFI <5cm, or deepest amniotic pocket <2cm

83
Q

How is polyhydramnios defined on scan?

A

AFI >25cm, or deepest amniotic pocket <8cm

84
Q

What is a normal endometrial thickness in women in their reproductive years?

A

5-14mm

85
Q

What is a normal endometrial thickness in post-menopausal women?

A

<4mm

86
Q

What is the maximum diameter or a pre-ovulatory ovarian follicle?

A

25mm

87
Q

What is the SI unit of abdorbed dose of ionising radiation?

A

Gray 9Gy)

88
Q

What is the SI unti of equivalent dose of ionising radiation?

A

Sievert (Si)

89
Q

What is telsa?

A

SI unit of magnetic strength

90
Q

What is Becquerel?

A

SI unit of radioactive decay

91
Q

When does a gestational sac become visible on TVS?

A

4+3/40, it is 3mm when visible

92
Q

When does a yolk sac become visible on TVS?

A

5-5+3/40, it is 3mm when it becomes visible and the gestational sac is 10mm

93
Q

When does the embryonic pole become visible on TVS?

A

5+3-6/40, it is 3mm when it becomes visible and the gestational sac is 16mm

94
Q

When can the yolk sac be seen on transabdominal scan?

A

When the gestational sac reaches 20m, i.e. at 7/40

95
Q

What are the 3 doppler modes?

A

1) Pulse; 2) Power; 3) Colour

96
Q

What are the main disadvantages of power doppler?

A

No information on a) direction or b) velocity of flow

97
Q

What are radiosensitizers?

A

They increase the effect of a given dose of radiation

98
Q

What are the four main groups of radiosensitizers?

A

1) Oxygen
2) Hypoxic cell sensitizers
3) Halogenated pyrimidines
4) Bioreductive agents

99
Q

What is the maximum normal diameter of the yolk sac on TVS?

A

6mm at 10/40. After 10/40 the yolk sac will gradually disappear. >6mm = suspicious for failed pregnancy

100
Q

What is the CXR equivalence to background radiation?

A

2.4 days

101
Q

What is the CT abdomen equivalence to background radiation?

A

2.7 years

102
Q

What might you see on ECG in hypercalcaemia?

A

Short QT

103
Q

What might you see on ECG in hypocalcaemia?

A

Long QT

104
Q

What is the SI for magnetic flux?

A

Weber

105
Q

On an ECG, what features would you likely see in WPW?

A

Short PR and delta waves

106
Q

What is the laser of choice in HPV or CIN?

A

CO2

107
Q

What is the laser of choice in TTTS?

A

Diode or ND:YAG

108
Q

What are the different types of solid sate laser?

A

Nd YAG; Neodynium; Titanium sapphire

109
Q

What are the different types of liquid laser?

A

Rodamine; Stibene; Coumarin

110
Q

What are the different types of semiconductor laser?

A

Diode

111
Q

What is the typical daily dose (fraction) of radiotherapy in cervical cancer?

A

1.8-2.0Gy

112
Q

What frequency is usually used in monopolar diathermy?

A

500kHz

113
Q

What is the mechanism of action of radiotherapy?

A

DNA damage via free radical generation

114
Q

Why does diathermy not use frequencies less than 200kHz?

A

Because lower frequencies may cause depolarisation and may cause electric shock.

115
Q

What is the typical magnetic field strength of an MRI scanner routinely used in the UK?

A

1.5-3.0T

116
Q

When does the fetal heart first become detectable on USS?

A

6/40

117
Q

At what time in the cycle of hystersalpingograms usually performed?

A

Day 6-12

118
Q

What is the normal axis of the heart?

A

-30 to +90 degrees

119
Q

What is T and Z scoring in DEXA scanning?

A

T score (compares the individual to a young adult where normal is greater than –1) and Z score (compares the individual to another individual of the same age and gender)

120
Q

Which laser in gynaecology surgery is invisible and cannot be transmitted down fibre optic cable?

A

Carbon dioxide

121
Q

At what temperature does necrosis occur?

A

44 oC

122
Q

At what temperature does coagulation occur?

A

70 oC

123
Q

At what temperature does desiccation occur?

A

90 oC

124
Q

At what temperature does carbonisation occur?

A

200 oC

125
Q

What can cause an elevated JVP with a normal waveform?

A

Right-sided heart failure

126
Q

At what hCG level should an experienced sonogropher be able to see an intrauterine gestational sac on transvaginal USS?

A

1000

127
Q

How does DEXA scanning work?

A

2 low dose X ray beams are emitted and the absorption of the soft tissue beam is subtracted from the total beam

128
Q

What is the penetration and resolution of transvaginal scanning relative to transabdominal scanning?

A

Transvaginal scanning = better resolution, worse penetration

129
Q

At what CRL would you expect to see a fetal heartbeat?

A

> 2mm

130
Q

How many x-ray beams are used in a DEXA scan?

A

x2 low-dose beams

131
Q

What does a T-score between +1 and -1 indicate?

A

Normality

132
Q

What does a T-score between -1 and -2.5 indicate?

A

Osteopenia

133
Q

What is reflection with regard to USS?

A

The change in direction of a waveform at an interface between two different media

134
Q

What is refraction?

A

Refraction is the change in direction of a wave due to a change in speed

135
Q

What is diffraction?

A

Bending of waves around small obstacles

Occurs when a wave encounters an obstacle that has a diameter comparible to its wavelength

136
Q

What factors effect doppler shift?

A
  1. Insonating frequency
  2. Velocity of moving blood
  3. Angle between sound beam and direction of moving blood
137
Q

What is USS unable to image?

A

Bone

Air

138
Q

What are the three different types of doppler?

A
  1. Pulse
  2. Power
  3. Colour
139
Q

What does pulse doppler provide information on?

A

1) Direction of flow
2) Velocity of flow
3) Flow characteritics

140
Q

What are the advantages of power doppler?

A

1) No angle dependancy
2) Higher sensitivity to detect low flow or small blood vessels
3) Better penetration

141
Q

What are the disadvantages of power doppler?

A

1) No directional flow

2) No velocity information

142
Q

What is the problem with pulse doppler?

A

It is angle dependant

143
Q

At what gestation does the fetal spine become visible?

A

> 9 weeks gestation

144
Q

What nuchal thickness is a problem?

A

> 6mm

145
Q

What is a nuchal thickness >6mm associated with?

A

Chromosomal abnormalities
Cardiac abnormalities
Fetal viral infection
Rhesus incompatibility

146
Q

What are the causes of polyhydramnios?

A

Increased fetal production - maternal DM, fetal anaemia, fetal AV malformation

Decreased fetal swallowing - UGI obstruction

147
Q

What is asymmetrical growth restriction due to?

A

Uteroplacental insufficiency

148
Q

What are the USS findings in uteroplacental insufficiency?

A

1) Uterine artery notches
2) Umbilical artery may have absent end-diastolic flow or reversed end diastolic flow
3) Fetal arterial redistribution

149
Q

What are the causes of oligohydramnios?

A

1) Uteroplacental insufficiency
2) Amniotic membrane rupture
3) Abnormal fetal renal function

150
Q

What is rachischisis?

A

Absence of neural tube

151
Q

What is lemon sign on USS?

A

Abnormal scalloping of the frontal bones

152
Q

What is banana sign on USS?

A

Crescent shaped cerebellum that produces

153
Q

When is the fetus most sensitive to radiation?

A

25 weeks gestation

154
Q

What is the radiation threshold for fetal malformation?

A

100-200mGy

155
Q

What is fractionation?

A

Time between radiation doses - allows normal cells time to recover between treatments
Allows time for re-oxygenation of hypoxic tumour cells between treatments

156
Q

What is the usual schedule of radiation in radiotherapy?

A

2Gy/day

157
Q

How do CTPA and V/Q compare in terms of risk?

A

CTPA carries an increased risk of breast cancer

V/Q scan has an increased fetal radiation dose - 3x greater than CTPA

MRCOG - Part 1 (13 decks)

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